NATURAL HISTORY

DESCRIPTION: The Moapa dace is olive-yellow on its upper side and white below. A distinguishing characteristic is a black spot at the base of its tail. It is about 4.5 to five inches long.

HABITAT: The species occurs in a variety of habitats in the upper Muddy River, including spring pools, spring outflows, and the main stem of the river. Its selection of habitat varies with its life stage. Larval dace are only found in the upper reaches of tributaries, where slack water can be found. Juveniles occur throughout available habitat, as do adults — though adults prefer the main stem of the river. These dace are found where water temperatures range from 67 to 90 degrees Fahrenheit.

RANGE: The Moapa dace is endemic to the Muddy River and its thermal springs within the Warm Springs area of Clark County, Nevada.

BREEDING: Although these dace reproduce year round, breeding peaks in the spring. This species matures at one year of age. Little is known about the reproductive characteristics of the dace.

LIFE CYCLE: Moapa dace are know to live for up to four years.

FEEDING HABITS: Moapa dace are omnivores, feeding on both plant and animal sources. They are known to eat things such as mayflies and caddisflies, worms, snails, plankton, algae, and bits of plants. These dace primarily wait for edible materials to come drifting by them, but adults will also search in the streambed gravels for food.

THREATS: Human activities have threatened the Moapa since the late 1800s, when settlers first inhabited the Moapa Valley and began using irrigation for agriculture. In the 1950s, several of the Muddy River's springs and tributaries — where Moapa dace swam — became swimming pools; some area springs and surface flow have been appropriated for municipal water supplies. Nonnative species such as shortfin mollies and blue tilapia not only impair dace habitat but also compete with the dace for food.

POPULATION TREND: The Moapa dace was first discovered in 1938 and was considered common until the 1950s. The population in 1969 was estimated to be 500 to 1,000 individuals; by 1983, at the time the species' original recovery plan was published, fewer than 1,000 individuals were found. In 1994, 3,841 adults were found, but by 2007 that number dropped to only 1,172 individuals. By 2010, the population had dwindled much further to include about 697 individual dace. That year, a fire almost completely destroyed the Warm Springs Oasis on the Muddy River, delivering what many believed could be a mortal blow to the fish's last remaining population.